In the coating of the convex side of an optical lens for blocking purposes, it is known from my U.S. Pat. No. 4,267,208 granted May 12, 1981, to dip the downwardly facing convex side of a lens into a solvent-containing liquid coating material, to upwardly withdraw the lens above the level of the coating material to drain excess coating material from the convex side of the lens, and to spin the lens about its vertical axis to centrifugually spread out the coating material as a continuous film covering the convex side of the lens. The dipping operation must be carefully observed so as only to coat the convex side of the lens without allowing the coating material to flow onto the concave side of the lens. Moreover, if there are air encapsulated bubbles at or near the surface of the coating material, these may be left on the convex side of the lens when upwardly withdrawn from the coating material and spun and may form pin holes or pressure points that can cause or contribute to a blemished lens surface from the hot metal blocking alloy cast thereagainst or from the heat and pressure during grinding the polishing of the concave surface of the blocked lens.
In said U.S. Pat. No. 4,267,208, a flexible squeeze bulb around the stem of the suction cup constitutes a releasable vacuum source for holding the lens for dipping and spinning but occasionally due to surface dust or lint, or airborne fibers or other foreign matter on the concave side of the lens or due to raised characters on the concave side of glass lenses, there may be sufficient leakage between the suction cup and the lens to inadvertently drop the lens during the coating operation with possible damage to the lens or dropping of the lens into the coating material with resulting time-consuming cleaning operations. In the case of lenses having foreign matter or raised characters on the concave side the leakage problem is eliminated by using a special suction cup having a soft pliable sealing gasket as disclosed in my copending application U.S. Ser. No. 164,235, filed June 30, 1980, now U.S. Pat. No. 4,356,989.